I use Laravel because you don't have to re-invent the wheel when compared to core PHP. We can focus directly on business logic. And the little learning curve for Laravel is worth it. Can't really compare with Laravel with Symfony as I haven't worked with Symfony yet. My suggestion would be to pick one and stick to it. If at all you have to move to other, it should be easy. Last thing I would like to add is that there are more people around who knows Laravel compared to PHP, may be that's why I started with Laravel.
I use Laravel because it has integrated unit testing that making TDD a breeze. Having a View (Blade engine) making me easier to work without too many efforts in front-end.
I do recommend going into the root of programming once getting stable on any framework. Go beyond Symfony, go beyond PHP, go into the roots to the mother of programming; c++, c, smalltalk, erlang OTP. Understand the fundamental principle of abstraction.
A framework is just a framework, it helps in getting feedback quickly; like practicing dancing in front of a mirror. Getting fundamentals right is the one true key in doing it right. Programming is not hard, but abstract-programming is extremely hard.